The first major step in the cheese making process is the coagulation of the milk by enzymatic hydrolysis of K-casein. To achieve this end, enzyme extracts from calf stomachs, microbially produced enzymes or other enzymes are utilized. The hydrolysis of K-casein leads to destabilization of the colloidal system of the milk. This is followed by aggregation of the micelles into clusters. Over time, the clusters grow in size. This growth in size is followed by crosslinking between chains which eventually transforms the milk into a gel or coagulum.
Once a desired point is reached in the coagulation process, the coagulum is "cut" by traversing with wire knives to slice the coagulum into approximately 0.7 cm cubes. The coagulating matrix then shrinks during further processing and as a result forces liquid from the cubes. Consequently, a two phase system of curd and whey results. The textural strength or firmness of the curd increases with time.
Selection of the optimum point to cut the coagulum has been a subject of much research. It has been shown that coagulum strength at cutting effects the recovery of milk components during cheese making. More particularly, milk components not entrapped in the K-casein matrix are lost into the whey. Thus, cutting the coagulum when extremely soft decreases cheese yield due to the increased loss of fat and curd fines. Conversely, cutting when the coagulum is too firm retards syneresis and results in high moisture cheese. Further, it has also been suggested that coagulum strength affects the quality of the resulting cheese.
Curd firmness and the rate of firming are affected by many factors. For example, high K-casein concentration increases curd firmness. The time and temperature of milk storage prior to cheese manufacture also affects curd firmness. Homogenization and standardization may also influence coagulum firmness. Other factors affecting firmness are the breed of cow from which milk is collected, period of lactation of the cow, milk quality and type of enzyme used in cheese making.
Cheese makers conventionally cut the coagulum 25 to 30 minutes after adding the enzyme to conform to factory schedules. As indicated above, however, the factors that influence firmness vary depending on milk source and treatments. Thus, coagulum cut 30 minutes after enzyme addition may not always be of a consistent strength. As a result, a need is identified for a sensor which will monitor milk coagulation and compensate for fluctuations in pH, temperature, enzyme activity, differences in milk and other relevant factors to allow the coagulum to be cut at a consistent condition near the optimum point for cheese production. In this way losses may be prevented due to inadequate enzyme addition and other factors may be addressed to increase overall yields.
To meet this need, a number of devices have been employed to measure coagulum strength with the object of predicting the cut-time. One such device is disclosed in U.S. Pat. No. 4,542,645 to Richardson et al. The apparatus disclosed in the Richardson et al. patent includes a substantially flat dish-shaped probe member that is suspended from a wire by a connecting rod into a enzymatic hydrolysis vessel filled with milk. The probe is reciprocated through a small vertical distance within the coagulating milk in the vessel. The increasing resistance to the probe manipulation is communicated through the wire as the milk coagulates. The resistance is measured and when it reaches a predetermined value, it is time to cut the coagulum.
While providing some guidance in establishing when to cut the coagulum, the Richardson et al. device unfortunately physically disrupts the coagulum and is sensitive to environmental vibrations. As such, it does not always provide a fully accurate measurement of coagulation and is considered a destructive test. Preferably, a continuous monitor should be non-destructive and accordingly, a need is identified for just such a monitor.